The invention relates to a projection screen having a light-absorbing layer.
In such a projection screen, which is known from European patent application EP-A2-0 421 809, a number of layers are located in front of the light-absorbing layer, each having a reflective effect for a color of light and a transparent effect for other colors of light. It is thereby envisaged to enhance the contrast between incident projected light and ambient light so that a brighter projected image is obtained.
However, the known projection screen has the drawback that it has a relatively complicated structure due to the large number of layers.
A further drawback is that the known projection screen has a great viewing angle dependence, i.e. the image quality is greatly dependent on the angle at which the screen is viewed, which may vary considerably.
It is an object of the invention to provide a projection screen in which an enhanced contrast between incident projected light and ambient light can be obtained in a simpler manner.
In the projection screen according to the invention, this object is achieved in that the projection screen is further provided with an active layer located in front of the light-absorbing layer, which active layer is transparent to light having a first direction of polarization and scatters light having a second direction of polarization.
By projecting light having a second direction of polarization on the projection screen, this light is scattered by the active layer, which is also referred to as scattering polarizer, in all directions, among which all of the directions remote from the light-absorbing layer. The daylight incident on the projection screen comprises both light having the first direction of polarization and light having the second direction of polarization. The light having the first direction of polarization is passed by the active layer and subsequently absorbed by the light-absorbing layer. The light having the second direction of polarization is scattered, similarly as the light from the projector.
An embodiment of the projection screen according to the invention is characterized in that a reflective polarizing layer is located between the light-absorbing layer and the active layer, which reflective polarizing layer is transparent to light having the first direction of polarization and reflective to light having the second direction of polarization.
The light having the second direction of polarization, scattered by the active layer towards the light-absorbing layer, is reflected by the reflective polarizing layer towards the active layer where it is again scattered, inter alia, in a direction remote from the absorbing layer.
A further embodiment of the projection screen according to the invention is characterized in that a micro-lens layer is located on a side of the active layer remote from the light-absorbing layer, the active layer being alternately provided with light-transmitting portions and scattering portions which scatter light having a second direction of polarization, while light can be directed onto the light-transmitting portions at a first angle of incidence and light can be directed on the scattering portions at a second angle of incidence by means of the micro-lens layer.
Such a projection screen is suitable if the projector is placed, for example, right opposite the projection screen, as a result of which the projected light from the projector is given a second angle of incidence. The ambient light is incident from all directions on the projection screen and thus comprises, inter alia, light directed onto the projection screen at a first angle of incidence. It will be evident that this first angle of incidence may comprise several angles deviating from the second angle of incidence. In the projection screen according to the invention, ambient light is directed at a first angle of incidence onto the light-absorbing layer via the light-transmitting portions. The light coming from the projector and having a second angle of incidence is directed onto the scattering portions by means of the lenses and scattered by these scattering portions in the same way as described hereinbefore. If desired, reflective polarizing portions may be positioned between the light-absorbing layer and the scattering portions, similarly as described hereinbefore.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.